Since his pipe size of 2 3/8" does not seem standard, the only thing to use for comparison is the Annulus cross-sectional area of the pipe and to have the same in two pipes calculates to 1 1/4". Just a tad over in area.
I would not necessarily call 13 gauge structural, but all depends what it is for.
To compare it with schedule 40 steel pipe of 2 1/2" in size or PVC it would be 6 gauge or 3/16" wall thickness or .203 inches. wall thickness changes with pipe sizes although still called schedule 40, and steel and PVC wall thickness are in respect with each other.
Raymond is correct that the webbing has a huge part in strength. However small spans such as the one pictured in the bottom right in this pagedo not use webs.
12 to 14 gauge is the common thickness for the tubing in these structures.
Can you really look at the crossectional area? A piece of dimensional lumber, say a 2x10 layed on edge can carry much more load than if it lays flat - yet it have the same cross sectional area either way.
Do you also think two 2x4’s would equal one 2x8?
Three 2x4’s would not even equal one 2x8…
The answer is x > 1 3/4 inches by applying common sense.
The equations for this would be mind boggling in their entirety.
There may be a shortcut method equation that some one developed but I doubt it. Pipes make lousy beams.
The question had no relative importance to framing or structural importance, all it asked was what was comparable to a 2 3/8 " distributed load over a given span. No mention if steel, PVC or otherwise.
I knew Paul was tricking us. See how you are Paul?? ha. ha.
At least I got an education out of it, by having to do the research on pipes sectional capacities. Paul is no fool, he knew he would get some of us going and I was the first one to grab on to it. ha. ha.
Only if you have no conception on how they can be designed to function as carrying members. Example: 2 x 4 top chord of a wood truss replaced the conventional 2 x 8 !!
That is because the effective span was reduced from the the ridge to the wall to just the span from one web intersection to another web intersection.
Also in a web some members are only under tension and some members are only under compression. In a solid beam the top is typically under compression and the bottom under tention. The middle of the beam mostly just hold the two together and transfer the load from one one flange to the other. That is why you can remove more material from the center of a solid beam than from the top or bottom without greatly effecting its load capacity.
I’m sorry. I was thinking they were pipes below grade and the loading was from a road or something else…
If the “pipes” were structural members, then the section properties would need to be looked at. And at the moment section properties of steel pipes doesn’t compute…
If it was just straight bending of tube steel, the calculations would be fairly simple for a structural engineer using equivalent section modulus methods. However the example use noted is in an arch that also involves bending, compression, and deflection which would involve some time to calculate out.
I could show you guys the formulas for calculating equivalent section modulus, arch cord compression stresses, and curved frame member deflection if ya would really like to have some fun and make your head spin … :twisted:
(P.S. Would prob have to scan in a few pages from the AISC manual, tube steel properties tables, and a bunch of pages from Rourke’s Formulas for Stress and Strain … but you will probably get a headache if ya don’t know what you are looking at … and that would probably be after a few days of pulling your hair out trying to figure out what the he!! they mean … )
The moment of inertia of a circle varies with the 4th power of its diameter (it is a cubed function for a rectangle). So the answer is (((2.375)^4)/2)^-4 or approximately 1.997".
Moment of Inertia (I) relates to a members stiffness … for things such as compression, buckling and deflections. For bending only from the original question (if only bending is involved, which does not appear to be the case), then the correct property to compare would the Section Modulus (S).
Also consider that it’s for structural pipe, which is hollow inside … that complicates things, and a straight comparison of circular sections wouldn’t be correct.
For Pipe, some of the parameters you will need/compare are:
I = 0.0491 x (D^4 - d^4)
S = 0.0982 x (D^4 - d^4) / D
r = (D^2 + d^2)^0.5 / 4
Where D = outside diameter and d = inside diameter
Without even considering that it’s an arch which complicates things (including possibly curved members, stability/buckling issues, compression and bending combination, and eccentric loading) you will probably also need some of the formulas from the AISC Manual and some of the formulas here … http://www.ce-ref.com/steel.htm … that is assuming the members are steel, and not aluminum or some other material.
This is for educational purposes only! … so have fun Marcel …
Well … normally I wouldn’t even scratch the surface of those issues, and would try to keep it in practial terms that would relate to home inspections. But, Marcel asked for it, so he got it … :twisted:
Hi. Robert;
[size=2]Since you are the expert, I guess you need to help me with this one. ha. ha. [/size]
(W) Load… The amount of pressure or force applied to a body to make it move or bend. (d) Deflection… The distance a part will move or bend when (W) is applied to it. (I) Moment of Inertia… Standard formulas for calculating the actions of material particles of area or mass using their locations from a reference axis. (E) Modulus of Elasticity… The ratio of stress to strain within proportional limits of a material, usually in tension or compression. Elastic Limit… The maximum point at which a material can be bent and then return to normal shape. Yield Point… The point on a stress-strain curve at which a material will no longer return to normal and instead, will stay deformed or break.
(L) **Length of beam **The length of the beam being used for the calculation. In our case, a pole for martin housing. Convert this dimension to inches, since the result we want to know is inches. Geometric shape… Round… Square… Triangular… Size… Large… Small… Material… Steel… Aluminum… PVC… Wood…
They look like similar formulas for the stiffness/deflection part of the example topic related to moment of inertia (I) - see above. Only one piece of the puzzle. And the defelection calculation are not for what I assumed was a simply supported member … but then again if it’s part of a frame the you would need the Rourke’s Formulas for Stress and Strain equations, or a computer program. You could assume simple end conditions for an example … even though that wouldn’t be correct for a space frame/arch.
)